The goal of the research in this proposal is to identify a Salmonella HIV-1 DNA vaccine vector configuration that induces durable, high-titer neutralizing antibody responses to HIV-1 in the mucosal and systemic immune compartments. The capacity of Salmonella vectors to deliver DNA vaccines and induce immune responses in the mucosal and systemic compartments supports the idea to deploy this vector to deliver DNA vaccines that express conformationally constrained HIV-1 Env immunogens. Moreover, strong humoral responses to gp120 developed in mice primed with a Salmonella gp120 DNA vaccine vector following two parenteral booster vaccinations with gp120 protein;in contrast, no such responses occurred in mice primed with the control Salmonella construct and boosted twice with gp120 protein (Section 3.3). The significance of having identified an effective vaccination protocol for the induction of high-titer antibody responses to a model HIV-1 antigen following a mucosal prime will not be overlooked. However, the Principal Investigator (PI) proposes that the complete utilization of this inexpensive oral vaccine vector necessitates that such responses arise without a heterologous vaccine modality boosts. In this regard, the responses induced by a first-generation Salmonella Env/gp120 DNA vaccine vectors to HIV-1 were predominantly cell-mediated ((1);App. 1). Nonetheless, the afore mentioned humoral priming attribute suggests the occurrence of low-dose immunogen expression, which induced memory T helper and B cell responses (12-16). By extension, the central hypothesis of this proposal is that the magnitude of the antibody responses to HIV-1 following vaccination with a Salmonella HIV-1 DNA vaccine vector is directly linked to the efficiency DNA vaccine delivery and immunogen expression in host cells. To test this hypothesis the potency and duration of mucosal and systemic antibody responses will be measured in mice vaccinated with Salmonella vectors that carry modifications designed to optimize DNA vaccine delivery and immunogen expression. It is projected that this approach will provide fundamental information germane to the development of an inexpensive oral HIV-1 vaccine.